Blood Typing Facts and Statistics

Q: What does forward blood typing mean?
Q: What does the above mean for transfusions?
Q: Statistically, What is the Blood Type Frequency percentage?
Q: What about the statistical percentage of Blood Type and Rh factor?
Q: If both parents blood type is known, what are the possible blood types of their children?
Q: How does Rh factor affect the giving of blood transfusions?
Q. Why is blood typing important?
Q. What is alloimunization?
Q. What is a rare blood type?
Q. What is the universal donor?
Q. Why do so many people who have had routine medical care not know their blood type?

Q: What does forward blood typing mean?
A: In forward typing a sample of the blood is mixed with serum that contains antibodies against type A blood ("anti-A serum"). Another sample of blood is then mixed with serum that contains antibodies against type B blood ("anti-B serum"). Finally another blood sample is mixed with serum that contains antibodies against type Rh Positive Blood ("anti-Rh serum). Patterns of clotting are then observed and recorded as follows:

Q: What does the above mean for transfusions?
A: Persons with type A blood can receive blood transfusions from donors with type A or type O blood.
Persons with type B blood can receive transfusions from donors with type B or type O blood.
Persons with type AB blood can receive transfusions from donors with type AB, type A, type B, or type O blood.

Q: Statistically, What is the Blood Type Frequency percentage?
A: Blood Type frequency in percentage of total population:

Q: What about the statistical percentage of Blood Type and Rh factor?
A: The overall statistical distribution of blood type plus Rh factor in the total population is as follows:

Note: Percentage distribution may be different within specific racial and ethnic subgroup

Q: If both parents blood type is known, what are the possible blood types of their children?
A: Blood type is determined by the "alleles" that are inherited from the parents. Alleles are possible types of a particular gene, in this case the blood type gene. There are three basic blood type alleles: A, B, and O. Children have two alleles, one inherited from each parent. The possible combinations of the three alleles are OO, AO, BO, AB, AA, and BB.

Blood types A and B are called co-dominant alleles, while O is recessive. A co-dominant allele is apparent even if only one is present; a recessive allele is apparent only if two recessive alleles are present. Since blood type O is recessive, it is not apparent if the person inherits an A or B allele along with it. Therefore, the possible allele combinations result in a particular blood type in this way:

Consequently, a person with blood type B may have a B and an O allele, or they may have two B alleles. If both parents are blood type B and both have a B and a recessive O, then their children will either be BB (if each parent passed on the B allele), BO (if one parent passed on B and the other parent passed on O), or OO (if both parents passed on the O allele). If the child is BB or BO, they have blood type B. If the child is OO, they will have blood type O.

When these basic blood type genetics are understood, then it becomes relatively easy to understand that it is not at all unusual for two parents with blood type B (or blood type A) to have children with blood type O.

Similar to A,B,O and AB blood types, Rhesus Factor (Rh +/-) genetics is determined from the possible allele combinations inherited from each parent. The DNA of each parent carries two Rh alleles either positive (+) or negative (-). The positive Rh factor allele is dominant over the negative Rh factor allele meaning that if a parent's pair of Rh factor alleles are one positive (+) and one negative (-), the positive allele will dominate the negative allele and result in a positive Rh factor (Rh+). Therefore it is quite possible that two parents with Rh+ factors to produce an Rh- child. Possible combinations are shown below:

Q: How does Rh factor affect the giving of blood transfusions?
A: Persons with Rh-positive blood can receive transfusions from donors with Rh-positive and Rh-negative blood.
Persons with Rh-negative blood can only receive transfusions from donors with Rh-negative blood.

Q. Why is blood typing important?
A. When the body is exposed to something foreign, like a blood transfusion, our immune system kicks in to protect us. One weapon the body deploys is the production of antibodies, protein molecules released by plasma cells that bind to a specific antigen. The antibodies couple with the antigens on the surface of the invading cells and try to destroy the cells. A cross-match is performed between the donor's blood and patient's blood to prevent this kind of reaction, which can range from mild to very serious. Antigens are also found on white cells and platelets. Additional testing, such as HLA testing or filtering may be performed in the case of white cell or platelet transfusion.

Q. What is alloimunization?
A. Most people, on average, will only need blood one time in their lives, to help fight a disease, restore blood lost during surgery or because of traumatic injury. But some patients, like sickle cell patients, may need blood many times during their lives. If the blood they receive is not a very close match, they will begin to reject transfusions, and an important source of help and hope will be gone. To prevent that, blood for these patients should be closely matched. Often, this will be a rare blood type. For sickle cell patients, the best match will come from donors of African descent. Fully one third of requests for rare blood received by the Red Cross is for a blood type found exclusively among African Americans.

Q. What is a rare blood type?
A. Some patients require rare blood types found in only one in 1,000 donors, or even less frequently. Through the American Rare Blood Donor Registry donors can be identified who have these rare blood types. When a need for their special blood type arises, the blood bank can call upon this donor to give blood. The Red Cross also freezes some rare units of red cells to assure their availability in a time of need.

Q. What is the universal donor?
A. Type O negative donors are known as universal donors because their blood may be transfused to patients of any other blood type in an emergency situation or if the specific needed blood type is unavailable. Because any patient can receive O negative blood, there is a constant need for O negative donors to give more often and shortages of type O blood can have critical consequences in national disasters. Whatever a person's blood type, they can be very important to someone in emergency crisis.

Q. Why do so many people (estimated at 70% of the population), who have had routine medical care not know their blood type?
A. Because they don't ask. Also there is the notorious reluctance among medical professionals to inform patients of their chart details.